1. Field of the Invention
This invention relates to a method of and an apparatus for measuring the roughness of the inner surface of a fine tube, and more particularly to a method of and an apparatus for non-destructively measuring the roughness of the inner surface of a gas supplying fine tube, for example, for a semiconductor manufacturing equipment.
2. Description of the Related Art
In a semiconductor manufacturing equipment, fine circuit patterns are formed in a plurality of layers on a silicon wafer serving as a substrate making use of the technique of photoengraving to form a circuit on the silicon wafer. The width of the circuit patterns is as fine as approximately 1 .mu.m, and in order to form such fine circuit patterns, it is important to keep the inside of the semiconductor manufacturing equipment clean. Thus, in order to prevent admission of fine dust into the semiconductor manufacturing equipment, the inner surface of a fine tube for supplying raw material gas for formation of circuit patterns therethrough is worked by mirror surface working to prevent such a trouble that dust sticks to bottom portions of the unevenness of the inner surface of the fine tube and is admitted into the semiconductor manufacturing equipment together with raw material gas.
In order to secure the quality of the inner surface roughness of fine tubes for a semiconductor manufacturing equipment, a fine tube inner surface roughness evaluation technique is employed wherein a fine tube sampled out for measurement of the inner surface roughness is divided longitudinally in an axial direction and the inner surface of a test piece obtained by such longitudinal division is measured by means of a surface roughness tester of the contact type.
In the contact type fine tube inner surface roughness evaluation technique, since the inner surface of the test piece as an object for measurement is a curved surface having a small radius of curvature, stable measurement of the inner surface roughness is impossible. Further, the test piece thus measured is manufactured for a sample test from among fine tubes to be used actually, and there is a problem in that the quality of fine tubes to be used actually cannot be secured. Therefore, a measurement method by which the inner surface roughness of a fine tube to be used actually can be non-destructively tested is demanded.